Mount St. Helens: Order from Mayhem
On the morning of May 18, 1980, after a century and a quarter of quiescence, a magnitude 5.2 earthquake triggered the explosive eruption of Mount St.Helens. The volcano's northern face collapsed, burying Spirit Lake and the headwaters of the Toutle River beneath hundreds of feet of avalanche debris. The accompanying blast sent winds of 600 mph and 400 to 600 degrees Fahrenheit sweeping across the landscape, leveling forests, vaporizing foliage, and searing soils. When the smoke and ash cleared, more than 240 square miles of forest north of the peak had been felled. A fringe of standing, dead, ash-covered trees formed a "ghost forest" around the blow down, and the ground was blanketed with tephra and ash.
When ecologist Peter Frenzen flew over the blast zone shortly after the eruption, he was struck by the scale of the destruction. Valley after valley, ridge upon ridge, were strewn with downed trees and ash. As he looked down over what appeared to be a scorched and lifeless landscape, Frenzen recalls feeling overwhelmed, but excited, too. Before the eruption, he had studied forest recovery on Mount Rainier's Kautz Creek mudflow, which dated from 1947, but this was a disturbance of a different order of magnitude.
Now, 18 years after the eruption, Frenzen and other researchers continue to make exciting discoveries at Mount St. Helens. What they are learning there about the ways that a forest recovers holds promise for the ecological restoration of logged-over forests throughout the Pacific Northwest.
Scientists see natural disturbances like the Mount St. Helens eruption as essential to ecological process. Unlike industrial clearcuts, most natural disturbances, such as wildfires, windstorms, infestations, and disease, are selective. They don't claim every tree. By creating new habitats and initiating forest succession, they play a key role in maintaining biological diversity in the forest. In the words of one ecologist, disturbance drives forest ecosystems.
In the Pacific Northwest, at least in this century, the Mount St. Helens eruption is the mother of all disturbances. By creating a range of altered habitats across a wide and varied landscape - from the sterilized Pumice Plain just north of the crater to the ghost forest of standing snags surrounding the blast zone - the volcano fashioned a magnificent laboratory for monitoring ecosystem recovery.
When Frenzen and other researchers first visited the blast zone on the ground, they were struck by how much life from the pre eruption forest had survived. Pocket gophers, deer mice, and other below-ground dwellers weathered the blast, as did large numbers of ground-dwelling insects and spiders. That summer, as high-country lakes emerged from under ice and the late snow pack melted back from north-facing ridges, whole communities of plants and animals emerged unscathed. Even in the heart of the blown-down forest, plants lifted above the ash in the soil that clung to upturned tree roots. And streamside willows, washed clean of debris by swollen rivers, traced a faint network of green across the ashen landscape.
Recovery began almost immediately," Frenzen recalls, "but it proceeded at different rates in different disturbance areas." One constant Frenzen found through out the blast zone was that the rate of recovery was closely tied to what remained from the original forest.
Ecologist Jerry Franklin of the University of Washington, who led the post eruption research team at St.Helens, calls the bits and pieces that survive a disturbance the forest's biological legacy." They are critical in initiating new growth and fostering recolonization by wildlife. At St. Helens, the legacy includes buried roots and bulbs, seedlings and shrubs protected by snow banks, streamside willows, standing snags, and of course, a multitude of downed trees.
St. Helens was central to our understanding of retention of biological legacies in natural disturbances," Franklin told me. "It was the most important lesson we learned there." This pivotal realization of the importance of biological legacies became the basis of Franklin's thinking about a more ecologically sound approach to forestry.
Franklin's vision of retention forestry replaces traditional clearcuts, where everything is taken, with more selective cutting, which leaves standing snags, downed logs, and representative patches of intact forest. Some of his ideas were incorporated into the Northwest Forest Plan and in government forestry policies in British Columbia and Chile. The forest industry has been slower to embrace the new science, but at least one logging company in the Northwest - Plum Creek Timber Co. - has brought Franklin's ideas into corporate boardrooms. Other ecologists, wildlife biologists, and foresters are still drawing insights from the recovery of the blast zone as it plays out in the protected area of Mount St.Helens National Volcanic Monument.
In 1982, Congress created the 110,000-acre monument and placed it under Forest Service management. Within monument boundaries, ecological recovery proceeds at its natural pace. The areas furthest along in this process are north-facing slopes that were protected by snow during the eruption. There, the small, shade-tolerant trees of the forest understory silver firs and western and mountain hemlocks - have flourished. But the pace of recovery is accelerating throughout the blast zone, as young trees cast seeds and spread across the landscape. Frenzen reports that conifers show robust growth and alders form 20- to 25- foot-high glades along floodplains. When you walk through these areas now, the canopy is well over your head," Frenzen told me. "You're literally in an alder forest." Even on the Pumice Plain, an area directly north of the crater that was blasted by pumice and gases reaching 1,200 degrees Fahrenheit, nearly a dozen tree species have seeded in, and the willow and alder shrub layer is creating the beginnings of a diverse forest.
Wildlife, too, is recovering by leaps and bounds. More than 34 species of birds and mammals have been identified on the Pumice Plain alone, and wildlife numbers spiral upward throughout the blast area as returning forests take hold.
Ecologist Charlie Crisafulli monitors the return of wildlife to the blast zone for the monument. He describes bird life on the Pumice Plain as an unexpected mix of species from a number of different habitats. High-country species like American pipits and gray-crowned rosy finches are found there, along with birds common to the Great Basin, such as horned larks and rock wrens. Birds more often seen in lowland meadows and pastures, like meadowlarks and savanna sparrows, flit past denizens of wetlands such as red-wing blackbirds. Crisafulli reports finding small mammals - mice, shrews, and voles - that venture out onto the Pumice Plain and fill habitat niches almost as soon as they become available. Their predators, weasels and hawks among them, soon follow. And in the early 1990s, a flock of Canada geese found its way to Spirit Lake; now a flock of up to 75 returns to nest on the plain each spring. "Eventually, some of these species will disappear as forest succession proceeds and conditions change," Crisafulli explains, "but new species will be continually added."
One of the most exciting wildlife developments in the blast zone occurred about 10 years after the eruption. Willows, alders, and cottonwoods growing along streams developed into the beginnings of a deciduous woodland, and a host of new birds began to appear. Many of these were "neotropical migrants, species that breed in temperate North America but over winter in the New World tropics. "As a group, these species have undergone dramatic declines in recent decades," Crisafulli told me. "We're seeing more species year by year as riparian areas develop, and we can begin to correlate species to habitat needs. We're even seeing some birds, like Vaux's swifts, that were believed to be dependent on old-growth forests. Because of the abundance of snags here, they're one of the most common birds in the blow down."
As different habitats are filled, scientists refine their sense of what is needed for any given species, and foresters using this data can fine-tune management strategies to increase natural diversity in managed stands.
Outside the national monument, on the multiple-use lands of the Gifford Pinchot National Forest, the blasted lands met a different fate. There, and on adjacent private forest lands owned by Weyerhaeuser Co., more than 1.5 billion board feet of blown-down trees were salvaged for timber, and approximately 10,000 acres were replanted with single-species stands of Douglas-fir. I was a partner in a tree planting company then, and our crew was part of a small army that followed in the wake of contract loggers, planting seedlings in the newly logged units. I remember steep, dusty hillsides and choked, rubble-strewn draws, and the thick layers of ash we dug through to reach plantable soil. Inspections were rigorous, and the distant whine of chain saws and yarders and the rumble from as many as 250 loaded logging trucks leaving the area each day created an incessant din. It was always a shock when I stopped and looked up from my work, to gaze out over thousands of acres of gray, barren ridges and draws. It took my breath away.
We did our work well, we and the dozens of other reforestation crews that replanted the salvaged cuts. The ash and pumice soil welcomed our seedlings, and today those hillsides and valley bottoms are thick with even-aged stands of Douglas-fir. In fact, they are so thick and so uniform that they provide an unsurpassed opportunity to experiment with techniques for managing early-succession forests to enhance their value as wildlife habitat.
Throughout the Northwest over the past half-century millions of acres of late-succession and old-growth forests have been liquidated by clear cutting and replaced with monocrop plantations of even-aged Douglas-fir. Biological legacies are for the most part absent in these plantations, and within a few decades, they close into dense stands that shade out deciduous brush and provide little habitat value for birds, deer and elk, and other wildlife.
One aspect of a long-term study being coordinated by the Forest Service's Pacific Northwest Research Station is designed to determine whether there are actions foresters can take with these young stands to hasten the development of late-successional habitat, increase the number of species found there, and promote a healthy mix of plant types.
Beginning in 1994, researchers established 25 16-acre plots in second-growth stands in the Clearwater Valley, just east of the monument, and began manipulating them in a variety of ways. Crews thinned trees, created openings of different sizes, and interplanted different species of trees and shrubs. Research forester Connie Harrington directs the study for the Forest Service's lab in Olympia, Wash. She stressed to me that the experiments are long-term and ongoing. "We'll be continually refining treatments and building on what we learn," she said. "We're already noting differences in tree growth and understory characteristics in some stands. In a few years, we'll go back and survey the plots for small mammals, amphibians, and birds; but it may take years, or even decades, before we can document measurable changes."
In the mean time, the bits and pieces of a functioning forest ecosystem are slowly reassembling themselves inside the monument. Ecologist Crisafulli reports that most of the small mammals that once inhabited the forest north of Mount St. Helens have already been recorded in the area, as have their predators. During field surveys last summer, he was amazed to find a snowshoe hare in an isolated wet meadow deep in the Pumice Plain, about 10 miles from the closest forest habitat. It becomes obvious at every turn that the ecosystem has been through this before. If there's a lesson to be drawn from the St. Helens experience, it's one of hope. As long as we keep all the cogs and wheels intact - to borrow Aldo Leopold's apt metaphor - the watch starts ticking anew.
Tim McNulty is a poet, conservationist, and nature writer who lives in the foothills of the Olympic Mountains of Washington state. His books include Olympic National Park: A Natural History and Washington's Mount Rainier National Park: A Centennial Celebration, published by The Mountaineers in Seattle.